Impregnated self-healing alternating voltage capacitor

ABSTRACT

An AC voltage capacitor employs a pair of layers of varnish with a metallic layer therebetween to form one electrode of the capacitor, the layer structure being carried by a second layer structure including a rough surface dielectric having metallic layers on both sides which are electrically connected together to form the other electrode of the capacitor.

D United States Patent [1 1 3,675,094 Voelkl July 4, 1972 [54]IMPREGNATED SELF-HEALING 1 References Cited ALTERNATING VOLTAGECAPACITOR UNITED STATES PATENTS I 1 Inventor: Waller Voelkl,v Munich, ay 3,248,620 4/1966 Haft et al. ..3l7/260 I ASSlgl'lCCI and [22] Filed:June 22 876,274 3/l953 Germany ..3l7/260 [2]] Appl. No.: 155,484 PrimaryExaminerE. A. Goldberg Att0meyl lil], Sherman, Meroni, Gross & Sim son[30] Foreign Application Priority Data [57] ABSTRACT June 25, 1970Germany ..P 20 31 741.3 An AC voltage capacitor employs a pair of layersof Varnish with a metallic layer therebetween to form one electrode of"317/258 1 6: the capacitor, the layer structure being carried by asecond [58] min ol earcli ii)is i o-25/25 42 mcluding a dielectrichaving metallic layers on both sides which are electrically connectedtogether to form the other electrode of the capacitor.

5 Claims, 3 Drawing Figures PATENTEDJUL 4 I972 3,675,094

INVEN'TOR M/a/fer Koe// BY ATTYS.

IMPREGNATED SELF-HEALING ALTERNATING VOLTAGE CAPACITOR BACKGROUND OF THEINVENTION 1 Field of the Invention This invention relates to animpregnated self-healing AC voltage capacitor, and is particularlyconcerned with such a capacitor wherein an electrode comprises a pair ofelectrically connected metallic layers between which there is providedan insulation material having a rough surface and/or porous compositionwherein the metallic layers are applied immediately to both surfaces ofthe insulating material.

2. Description of the Prior Art The German Pat. No. 832,640 discloses aself-healing coiled capacitor wherein each electrode thereof comprises apair of electrically connected metallic layers carried on a paper foil.The dielectric material of this particular capacitor consists, forexample, of polystyrene and the capacitor is not impregnated.

In a previously filed German patent application P 64 792.4 (S 107,565VIIIc/21g) an impregnated capacitor is disclosed which utilizes aplastic foil as the dielectric material. In this particular capacitor,the electrodes also consist of bilaterally metallized insulatingmaterial insertions. Each of these metallizations carried by the plasticfoil are electrically connected and the insulating material is thereforedisposed in a field-free area between these metal layers. This type ofcapacitor can be operated at high voltages. In case of a disruptivedischarge, there is a high energy flow to the point of disruptivedischarge.

SUMMARY OF THE lNVENTlON The primary object of the present inventionresides in the provision of a capacitor as initially described with astar-like micro fissure structure to limit the energy flow in case of adisruptive discharge to the point of discharge in one of themetallizations forming part of an electrode.

The foregoing objective is realized with the aid of a feature of thepresent invention which provides that along with the bilaterallymetallized insert of insulating material, two varnish layers and ametallic layer arranged therebetween are processed into a capacitor,whereby the metallic layer disposed between the two varnish layers formsthe counter electrode with respect to the two metallizations carried bythe insert of insulating material.

A micro fissure structure can be produced in the metallic layer that isdisposed between the two varnish layers acting as dielectric material.The varnish layer located below (as viewed in the drawings) the metalliclayer is swelled on or dissolved on by the solvent of the second varnishlayer. The intermediate metallic layer is tom up in a star-like patternby the swelling on process. The star-like pattern in the metallic layerlimits, in case of a disruptive discharge, the energy flowing to thepoint of disruptive discharge and thereby avoids distruction of theadjacent layers of the capacitor during the healing process.

The book by L. Holland Vacuum Deposition of Thin Films, London (1961),pages 367 to 369 discloses that a metal layer may be disadvantageouslytorn up when varnishing over a metal layer which has been applied tolacquer as determined in the plastic or automotive industry.

The capacitor design according to the present invention can be producedin that both varnish layers with the metallic layer therebetween aredesigned as thin foils, and during coiling or stacking, they are appliedto the bilaterally metallized insert of insulating material.

A second possibility for producing the capacitor according to thepresent invention provides that the varnish layers and the metalliclayer be applied consecutively to one of the metallized surfaces of theinsert of insulating material to form a single consistent layerarrangement. A single layer arrangement suffices to produce a capacitor,for example, by coiling whereby the possibility of automation of thewinding or coiling operation is decisively improved.

BRIEF DESCRIPTION or THE DRAWINGS Other objects, features and advantagesof the invention, its organization, construction and operation will bestbe understood from the following detailed description of exemplaryembodiments thereof taken in conjunction with the accompanying drawings,in which:

FIG. 1 is an exaggerated cross-sectional view of a capacitor which maybe in a coiled or stacked configuration wherein the bilaterallymetallized insert of insulating material is processed with a thin foilconsisting of two varnish layers and an intermediate metallic layerembedded therebetween;

FIG. 2 is an exaggerated cross-sectional view of a capacitor which maybe made in the form of a coil or stacked capacitor wherein a pair ofvarnish layers and an intermediate metallic layer are immediatelyapplied to a bilaterally metallized insert of insulating material; and

FIG. 3 is an exaggerated cross-sectional view of a capacitor accordingto the invention which may be made in either a coiled or stacked formand which has an internal series circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a capacitorstructure comprising a layer 1 of insulating material having a roughsurface and/or a porous composition, which layer may advantageouslyconsist of paper. The layer of insulating material 1 carries on oppositesides thereof a pair of metallizations or metallic layers 2,3. Themetallic layers 2 and 3 are seized for electrical contact by a contactlayer 7 which is applied to a frontal side of the capacitor to form ashort circuit. A pair of metal-free marginal strips l1, 12 are providedat the opposite frontal side of the capacitor for better insulation ofeach of the metal layers 2, 3. Both metal layers 2 and 3 form anelectrode of the capacitor. The other or counter electrode is formed bya metallic layer 4 which is located between a pair of varnish layers 5,6. Both of the varnish layers 5 and 6, and the interposed metallic layer4, are advantageously formed as a thin foil structure which is producedby being varnished or steamed on an auxiliary carrier foil from whichthe structure is removed for application to the capacitor structure. Themetallic layer 4 is seized for electrical contact at the aforementionedopposite frontal side by a second frontal contact layer 8. The metalliclayer 4 is insulated from the frontal side of the capacitor whichcarries the frontal contact layer 7 by the provision of a metal-freemarginal strip 13. The thin foil structure consisting of both varnishlayers 5, 6 and the metallic layer 4 located therebetween is coiled in astaggered manner with respect to the bilaterally metallized insulatinglayer 1, so that an improved contact is produced with the frontalcontact layers 7, 8 and an improved insulation of the metallic layerswith respect to these contact layers is also provided.

FIG. 2 likewise illustrates a bilaterally metallized insulating materialinsert 1 with a rough surface, which again may consist of paper. Themetallic layers 2, 3 which are directly applied to the layer 1 and whichare electrically connected together by a frontal contact layer 8 againform an electrode for the capacitor. These metallizations are insulatedwith respect to the frontal contact layer 7 on the opposite frontal sideof the capacitor by the provision of metal-free marginal strips l1, 12.The counter electrode is formed by a metallic layer 4 which is embeddedbetween a pair of varnish layers 5 and 6. The metallic layer 4 is seizedby the frontal contact layer 7 and is insulated from the frontal contactlayer 8 by the provision of a metal-free insulating marginal strip 13.In manufacturing the arrangement illustrated in this Figure, the varnishlayer 6 is applied directly to one of the metallized sides of theinsulating material layer 1, here to the layer 3, and the second varnishlayer 5 is applied thereover subsequent to the provision of the metalliclayer 4. When producing a coiled capacitor, only one layer structure ofthe type illustrated in FIG. 2 is necessary so that a single foilresults which considerably facilitates the possibility of employingautomated production techniques.

FIG. 3 illustrates a capacitor according to the present inventionwherein the metallic layers 2, 3 are applied on opposite sides of aninsulating material layer 1. The metallic layers 2 and 3 extend as faras both frontal surfaces of the capacitor at which points they areseized by the frontal contact layers 7 and 8 which serve to receive anapplication of reverse polarity.

The metallic layers 2 and 3 comprise continuous metal-free strips 14,which extend in the center of the capacitor parallel to the frontalsurfaces. Both halves of each of the metallic layers 2 and 3 areinsulated with respect to each other by these metal-free strips. Onehalf of each of the metallic layers 2 and 3 is gripped by the contactsurface 7 and the other halves of each of these layers are seized by thefrontal contact surface 8 which is to carry a reverse polarity. Themetallic layer disposed between the pair of varnish layers 5 and 6 formsa blind coat. The metallic layer 4 is not seized by either of thefrontal contact layers 7, 8 and is insulated from these contact layersby non-metallic strips 9 which extend parallel to the frontal contactsurfaces. An internal series circuit is provided in the capacitor designillustrated in FIG. 3. Both of the varnish layers 5, 6 may be placedwith the interposed metallic layer 4 as thin foils in the capacitor bodyor on one of the metallized surfaces of the insulating material 1 as animmediate application to such surface. The advantage of the embodimentillustrated in FIG. 3 resides in the fact that with the aid of theinternal series circuit, a 2-layer structure is accomplished with halfthe number of varnish applications. The capacitor design represented inFIG. 1 can be impregnated without any problem. An impregnating means canpenetrate the interior of the capacitor body without trouble from thefrontal sides into the air gaps formed between the rough surfaces of thelayer 1 and the smooth surfaces of the varnish layers 5 and 6.

In the structure represented in FIG. 2, the impregnating means canpenetrate through the air gaps between the unvarnished surface of theinsulating layer 1 bearing the metallic layer 2 and the smooth surfaceof the varnish layer 5 from the frontal sides into the interior of thecapacitor.

To produce the micro fissure structures in the metallic layers 4 and 4',the solvents for the varnish layers 5 and 5 must be so selected thatthey swell on or dissolve on the varnish layers 6 and 6'. By selectingacetyl cellulose for the varnish layers 6 and 6, low acetic acid estersare utilized as varnish solvent for the layers 5 and 5 Mixtures areapplicable particularly for varnish solvents which consist of about 50percent acetic acid methyl ester, about 45 percent acetic acid ethylester and about 5 percent methyl alcohol, also about 25 percent methylacetate, about 23 percent ethyl acetate, about 2 percent methanol andabout 50 percent methylene chloride. The acetyl cellulose varnishsolution has a solid body content of less than 10 percent and aviscosity in the order of 240 cP. The solid body content is selected inparticular at about 6 percent. Such solvents are described in a previousGerman patent application Ser. No. P 14 39 314.

The present invention makes possible an impregnated electrical capacitorwith high capacitive values comprising a varnish dielectric and isoperable for AC voltage applications and has good regenerativeproperties.

Although I have described my invention by reference to specificillustrative embodiments thereof, many changes and modifications maybecome apparent to those skilled in the art without departing from thespirit and scope of my invention, and it is to be understood that Iintend to include within the scope of the patent warranted hereon allsuch changes and modifications as may reasonably and properly beincluded within the scope of my contribution to the art.

I claim:

1. An impregnated self-healing AC voltage capacitor com prising a firstelectrode including a pair of parallel spaced electrically connectedmetallic layers and a rough surface layer of insulating materialcarrying said metallic layers, a first varnish layer disposed adjacentone of said metallic layers, a second varnish layer and a third metalliclayer forming a second electrode sandwiched between said first andsecond varnish layers.

2. A capacitor according to claim 1, wherein said first and secondvarnish layers and said third metallic layer are thin foils and saidfirst varnish layer adheres to said one metallic layer.

3. A capacitor according to claim 1, comprising metallic contact layers,said layer of said pair of metallic layers extending between saidcontact layers and including a gap therein to form pairs of side by sidemetallic layer portions, first nonmetallic strips extending across saidgaps to insulate said portions from each other and said non-metallicinsulation strips disposed between said third metallic layer and saidmetallic contact layers.

4. A method of making an AC voltage capacitor comprising the steps of:metallizing both sides of a rough surface dielectric layer, and applyingto one metallized surface a layer structure of a pair of varnish layershaving a metal layer therebetween.

5. The method of claim 4, further defined in that the step of applyingthe layer structure includes the steps of: applying a first layer ofvarnish to the one metallized surface, metallizing a layer on a portionof the first layer of varnish, and applying a second layer of varnishover the metallized layer and metalfree portions of the first layer ofvarnish.

1. An impregnated self-healing AC voltage capacitor comprising a firstelectrode including a pair of parallel spaced electrically connectedmetallic layers and a rough surface layer of insulating materialcarrying said metallic layers, a first varnish layer disposed adjacentone of said metallic layers, a second varnish layer and a third metalliclayer forming a second electrode sandwiched between said first andsecond varnish layers.
 2. A capacitor according to claim 1, wherein saidfirst and second varnish layers and said third metallic layer are thinfoils and said first varnish layer adheres to said one metallic layer.3. A capacitor according to claim 1, comprising metallic contact layers,said layer of said pair of metallic layers extending between saidcontact layers and including a gap therein to form pairs of side by sidemetallic layer portions, first non-metallic strips extending across saidgaps to insulate said portions from each other and said non-metallicinsulation strips disposed between said third metallic layer and saidmetallic contact layers.
 4. A method of making an AC voltage capacitorcomprising the steps of: metallizing both sides of a rough surfacedielectric layer, and applying to one metallized surface a layerstructure of a pair of varnish layers having a metal layer therebetween.5. The method of claim 4, further defined in that the step of applyingthe layer structure includes the steps of: applying a first layer ofvarnish to the one metallized surface, metallizing a layer on a portionof the first layer of varnish, and applying a second layer of varnishover the metallized layer and metal-free portions of the first layer ofvarnish.